Method of forming nozzle for injection device and method of manufacturing inkjet head

ABSTRACT

When a nozzle  21  with a stepwise cross-section, which is provided with a small cross-sectional nozzle portion  21   a  formed on the front side thereof and with a large cross-sectional nozzle portion  21   b  formed on the rear side thereof in a discharge direction, respectively, is formed by applying etching to a silicon wafer  200  for forming a nozzle plate  2 , a resist film  210  is formed on a surface  200   a  of the silicon wafer  200 , and patterning by half-etching and patterning by full-etching is applied to the resist film  210 . Next, anisotropic-dry-etching is applied to the silicon wafer  200  by ICP discharge, thereby forming grooves at the full-etched portions. Next, the resist film at the half-etched portions is removed and anisotropic-dry-etching is applied to the portions from which the resist film is removed by ICP discharge. As a result, there can be simply formed on a monocrystalline silicon substrate an ink nozzle having a stepwise cross-section and further having an action, which is larger than that of a conventional ink nozzle, for aligning the directions of pressures applied from cavities to nozzles in a nozzle axis direction.

TECHNICAL FIELD

The present invention relates to a method of forming a nozzle for anejection device for ejecting or spraying a liquid or a gas. Moreparticularly, the present invention relates to a method of forming anozzle having a cross-section which is made smaller stepwise toward thefront end thereof by etching a silicon monocrystalline substrate.Further more, the present invention relates to a method of forming anozzle plate which is preferable for an inkjet head for ejecting inkdroplets.

BACKGROUND ART

For example, the inkjet head of an inkjet printer generally comprises aplurality of nozzles for ejecting ink droplets therefrom and an inksupply passage communicating with the nozzles.

Recently, it has become necessary to more precisely and more minutelyprocess inkjet heads to permit ultrafine characters to be printed. Forthis purpose, there have been proposed many methods of forming microporenozzles by applying anisotropic-etching to a silicon substrate.

It is preferable to use a nozzle having such a cross-sectional shapethat a thin nozzle hole portion is formed on the front end side thereofand a nozzle hole portion expanding in a conical shape or a pyramidalshape is formed at the rear end side thereof in order to improve the inkejection characteristics of the respective nozzles of an inkjet head.For example, as disclosed in Japanese Unexamined Patent Publication No.56-135075, when a nozzle is formed in a cylindrical shape at the frontend side thereof and the inner periphery of the nozzle is formed in atruncated-quadrangular-prism shape at the rear side thereof, thedirections of ink pressures imposed on nozzles from an ink cavity sidecan be aligned in the axial directions of the nozzles, as compared witha case where cylindrical nozzles are used. Stable ink ejectioncharacteristics can be obtained thereby. That is, since variations inthe trajectories of ink droplets can be eliminated, they are preventedfrom flying in differing directions, whereby variations in the amount ofthe ink droplets can be suppressed.

As disclosed in Japanese Unexamined Patent Publication No. 56-135075,however, since the truncated-quadrangular-prism-shaped inner peripheryof the nozzle on the rear side is formed in a silicon substrate usinganisotropic-etching, the inner periphery is formed along the crystaldirection of the silicon. Thus, the angle of the inclined rear portionof the nozzle is reduced to obtain an action for aligning the directionsof ink pressures imposed on the nozzles from the ink cavity side in theaxial directions of the nozzles. That is, it is impossible to decreasethe cross-sectional area of the nozzle on the rear side thereof.

In contrast, for example, Japanese Unexamined Patent Publication No.5-50601, filed by the applicants, discloses a method of manufacturing anelectrostatic drive type inkjet head in which a nozzle and an ink supplypassage are formed with pinpoint accuracy by applying photolithographyand wet-type-crystal-anisotropic etching to a silicon monocrystallinesubstrate.

The inkjet head disclosed in the publication employs a structure inwhich nozzles, reservoirs, ink supply passages such as cavities and thelike, and diaphragms are formed on a silicon monocrystalline substratebonded to a glass electrode substrate, on which electrodes fordeflecting the diaphragms by electrostatic force are formed.

The use of this structure allows a manufacturing method to be employedin which after the patterns (nozzles, ink supply passages, electrodes)of respective inkjet heads are formed on the respective substrates, thesubstrates are bonded to each other and the thus-bonded substrates arecut and separated into the respective inkjet heads (the so-called methodof making multiple inkjet heads from a single substrate), whereby theinkjet heads can be manufactured at low cost. Note that an example ofthe method of making multiple inkjet heads from a single substrate isdisclosed in Japanese Unexamined Patent Publication No. 9-300630, filedby the applicants. Specifically, the publication proposes a method ofbonding a plurality of cover substrates and a flow passage substrate ina row state so that terminals formed at a lower substrate to supply asignal or power are exposed.

Incidentally, when nozzles are formed on a cover substrate for coveringan ink supply passage and the cover substrate itself is used as a nozzleplate, it is preferable for accuracy that after a single nozzle plate isbonded to a flow passage substrate, the combined substrate be separatedto respective inkjet heads, as compared with the method disclosed inJapanese Unexamined Patent Publication No. 9-300630.

In this case, a through-hole for exposing terminals formed on the lowersubstrate must be formed, in addition to the nozzles, on the nozzleplate as the uppermost substrate of these three substrates.

Etching is carried out at a relatively low rate in a process for formingnozzle holes because pinpoint processing accuracy is required in theprocess. In contrast, etching is carried out at a relatively high ratein a process for forming the through-hole whose accuracy is relativelynot as stringent as that for the nozzle holes because a reduction inetching time takes precedence over processing accuracy. As a result, theprocess for forming the nozzle holes and the process for forming thethrough-hole, the etching conditions of which are different from eachother, have ordinarily been performed independently from each other.That is, after the through-hole is formed by etching, the nozzle holesare etched; or after the nozzle holes are formed by etching, thethrough-hole etched.

Thus, all the sub-processes relating to the etching process, such aspatterning including the formation of a resist film, masking, and theremoval of the resist film, rinsing, and the like, must be carried outtwice, whereby problems arise in that the manufacturing process iscomplex and the manufacture is time-consuming.

Problems to be solved by the present invention, which was made in viewof the above points, primarily reside in the following two points:

1) to propose a method for forming a nozzle for an ejection device in amonocrystalline silicon substrate, the nozzle having a substantialaction for aligning the directions of pressures imposed on nozzles froma cavity side in the axial directions of the nozzles, as compared withthe action obtained by a conventional method; and

2) to propose a method for manufacturing an inkjet head capable offorming a nozzle without lowering the processing accuracy thereof, aswell as capable of forming a through-hole, which is very large relativeto the nozzle, on a monocrystalline silicon substrate simultaneouslywith the formation of the nozzle, thereby simplifying the manufacturingprocess and reducing manufacturing time.

Disclosure of the Invention

To solve the problem 1), the present invention employs a dry-etchingmethod by ICP (induction coupled plasma) discharge as an anisotropicdry-etching method to form a nozzle having a cross-section made smallerstepwise toward the front end thereof by applying etching to a siliconmonocrystalline substrate.

That is, in a method of forming a nozzle of the present invention,first, an oxidized silicon film, for example, is formed as a resist filmon a surface of the silicon monocrystalline substrate. Next, a firstopening pattern is formed by removing the resist film at a portioncorresponding to the rear end of the nozzle and a second opening patternwhich is smaller than the first pattern is formed by removing the resistfilm at a portion corresponding to the front end of the nozzle. Next,dry-etching is applied by plasma discharge to the exposed portions ofthe surface of the silicon monocrystalline substrate exposed by thefirst and second opening patterns. At this time, a gas for etchingsilicon by conversion to a plasma by plasma discharge and a gas forsuppressing the etching of silicon by conversion to a plasma by plasmadischarge are alternately charged into a processing vessel in which thesilicon substrate is disposed. With this processing, a nozzle is formedhaving a cross-section which coincides with the shapes of the respectiveopening patterns and is made smaller stepwise from the rear end thereoftoward the front end thereof.

Furthermore, when the respective opening patterns are formed asdescribed below, a nozzle whose cross-section is made smaller stepwisefrom the rear end thereof toward the front end thereof can be formed byperforming dry-etching only from one side of the silicon substrate,whereby the manufacturing process can be further simplified.

That is, after a resist film is formed on a surface of the siliconmonocrystalline substrate, the opening pattern, which corresponds to theportion of the nozzle at the rear end thereof, is formed at the resistfilm by half-etching the resist film (first patterning process). Next,an opening pattern which corresponds to the portion of the nozzle at thefront end thereof is formed as the exposed portion of the surface of thesilicon monocrystalline substrate by full-etching a portion of thehalf-etched region of the resist film at which the above opening patternis formed (second patterning process). Thereafter, a first groove havinga predetermined depth is formed by applying dry-etching to the exposedportion of the silicon monocrystalline substrate by plasma discharge(first dry-etching process). Then, after the surface of the siliconmonocrystalline substrate is exposed by full-etching the half-etchedregion of the resist film, a second groove having a predetermined depth,while the first groove remains on the bottom thereof, is formed byapplying dry-etching to the silicon monocrystalline substrate by plasmadischarge (second dry-etching process).

When anisotropic-dry-etching is started by plasma discharge in the firstdry-etching process, only the surface portion of the siliconmonocrystalline substrate whose surface is exposed by the full-etchingis vertically removed by the etching so that the first groove having apredetermined depth is formed. In the second dry-etching process, theetching of the surface of the silicon monocrystalline substrate isconducted in a state in which the first groove which was formed first bythe etching remains as it is, and the second groove is formed. Whenetching conditions are properly determined, the depth of the portion ofthe first groove can be set to a size which coincides with the nozzle atthe front end thereof having a small cross-section and the depth of theportion of the second groove can be set to a size which coincides withthe nozzle at the rear end thereof having a large cross-section.

According to the method, a master pattern need not be repeatedly formedon the surface of the silicon monocrystalline substrate. Further more, amaster pattern need not be formed along the surface of the siliconmonocrystalline substrate in the stepwise state after a recess is formedat the silicon monocrystalline substrate. Thus, according to the nozzleforming method of the present invention, the nozzle having thestepwise-cross-section can be effectively and simply formed.

To solve the problem 2), the present invention employs a method arrangedsuch that a first fine groove acting as the nozzle is formed up to apredetermined depth and a second groove acting as a part of athrough-hole, which exposes a terminal disposed on a substrate to bebonded to the lower side of a substrate serving as a nozzle plate, areformed from a surface of the substrate serving as the nozzle plate byetching. Thereafter, a third groove, larger than the first groove, isformed from the other surface of the upper substrate by etching, and thenozzle and the through-hole are simultaneously formed by penetrating thefirst groove and the second groove.

With this procedure, the through-hole can be formed simultaneously withthe nozzle without lowering processing accuracy. When the through-holeis relatively large, it is preferable to form the second groove byetching into a shape which follows the contour of the outer periphery ofthe through-hole. Since the etching area of the portion of thethrough-hole can be reduced thereby, the reduction of etching speed canbe prevented, and the deterioration of the accuracy of the grooves in adepth direction caused by the etching applied to a wafer surface can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an example of anelectrostatic rive type inkjet head to which a method of the presentinvention can be applied.

FIG. 2 is a schematic sectional view of the inkjet head shown in FIG. 1.

In FIG. 3(A) is an explanatory view showing a firstthermally-oxidized-film forming process in a manufacturing process of anozzle plate for the inkjet head in FIG. 1, FIG. 3(B) is an explanatoryview showing a first patterning process of a SiO₂ film in themanufacturing process, and (C) is an explanatory view showing a secondpatterning process of the SiO₂ film in the manufacturing process.

In FIG. 4(A) is an explanatory view showing a first dry-etching processapplied to a silicon wafer in the manufacturing process of the nozzleplate for the inkjet head in FIG. 1, FIG. 4(B) is an explanatory viewshowing a state after a half-etched-portion is removed in themanufacturing process,(C) is an explanatory view showing a seconddry-etching process FIG. 4 applied to the silicon wafer in themanufacturing process, and FIG. 4(D) is an explanatory view showing astate after the SiO₂ film is removed in the manufacturing process.

In FIG. 5(A) is an explanatory view showing a secondthermally-oxidized-film forming process in the manufacturing process ofthe nozzle plate for the inkjet head in FIG. 1, FIG. 5(B) is anexplanatory view showing a third patterning process of the SiO₂ film inthe manufacturing process, FIG. 5(C) is an explanatory view showing awet-etching process applied to the silicon wafer in the manufacturingprocess, and FIG. 5(D) is an explanatory view showing a state after theSiO₂ film is removed in the manufacturing process.

FIG. 6 is an explanatory view showing a final thermally-oxidized-filmforming process in the manufacturing process of the nozzle plate for theinkjet head in FIG. 1.

In FIG. 7(A) is an explanatory view showing a firstthermally-oxidized-film forming process in the manufacturing process ofanother embodiment of the nozzle plate for the inkjet head in FIG. 1,FIG. 7(B) is an explanatory view showing a first patterning process of aSiO₂ film in the manufacturing process, and FIG. 7(C) is an explanatoryview showing a second patterning process of the SiO₂ film in themanufacturing process.

In FIG. 8(A) is an explanatory view showing a first dry-etching processapplied to a silicon wafer in the manufacturing process of anotherembodiment of the nozzle plate for the inkjet head in FIG. 1, FIG. 8(B)is an explanatory view showing a state after a half-etched portion isremoved in the manufacturing process, FIG. 8(C) is an explanatory viewshowing a second dry-etching process applied to the silicon wafer in themanufacturing process, and FiG. 8(D) is an explanatory view showing astate after the SiO₂ film is removed in the manufacturing process.

In FIG. 9(A) is an explanatory view showing a secondthermally-oxidized-film forming process in the manufacturing process ofthe another embodiment of the nozzle plate for the inkjet head in FIG.1, FIG. 9(B) is an explanatory view showing a third patterning processof the SiO₂ film in the manufacturing process, FIG. 9(C) is anexplanatory view showing a wet-etching process applied to the siliconwafer in the manufacturing process, and FIG. 9(D) an explanatory viewshowing a state after the SiO₂ film is removed in the manufacturingprocess.

FIG. 10 is a graph showing the relationship between the aperture ratioof a silicon wafer and an etching speed in the dry-etching process of asilicon wafer.

BEST MODE FOR CARRYING OUT THE INVENTION Example of an inkjet head towhich the present invention is applied

FIG. 1 is an exploded perspective view of an inkjet head to which amethod of the present invention can be applied, and FIG. 2 shows aschematic cross-section of the inkjet head in FIG. 1.

Description below is made with reference to FIGS. 1 and 2; the inkjethead 1 of the example is an electrostatic drive type inkjet head similarto the inkjet head disclosed in Japanese Unexamined Patent PublicationNo. 5-50601, filed by the applicant. The inkjet head 1 is arranged bysimilarly bonding together a nozzle plate 2 (upper substrate) composedof a silicon monocrystalline substrate, a cavity plate 3 (first lowersubstrate) composed of a silicon monocrystalline substrate, and a glasssubstrate 4 (second lower substrate).

Note that while both figures show a single head to simplify description,patterns for a plurality of inkjet heads are formed on each of thesubstrates 2, 3, and 4. After the substrates are bonded together, theyare divided into individual inkjet heads by being cut by dicing alongplane C—C and plane D—D shown in FIG. 2.

A plurality of ink cavities 31 and a common ink reservoir 32 forsupplying ink to the respective ink cavities 31 are formed on the cavityplate 3. A plurality of nozzles 21 communicating with the respective inkcavities 31 and ink supply ports 22 for communicating the respective inkcavities 31 with the common ink reservoir 32 are formed in the nozzleplate 2. Each ink supply port 22 has a cross-sectional shape such that adeep groove portion 22 a is formed at one end thereof and a shallowgroove portion 22 b is formed at the other end thereof

Recesses 41 are formed on the glass substrate 4, which is bonded to theback surface of the cavity plate 3, at the portions thereof confrontingdiaphragms 33 which define the bottoms of the ink cavities 31.Individual electrodes 42 are formed on the bottoms of the recesses inconfrontation with the diaphragms 33.

The individual electrodes 42 are connected to individual terminals 42 bdisposed in recesses 45 through leads 42 a disposed in grooves 44.

A through-hole 36 is formed at the cavity plate 3 so that the individualterminals 42 b are exposed when the cavity plate 3 is bonded to theglass substrate 4. A common terminal 35 is disposed in the vicinity ofthe through-hole 36 to supply an electrical charge to the diaphragms 33.A through-hole 23 is also formed at the nozzle plate 2 to expose theindividual terminals 42 b and the common terminal 35 when nozzle plate 2is bonded to the lower substrate. After the bonded substrates aredivided into the individual inkjet heads, an FPC (not shown) isconnected to these individual terminals 42 b and 35.

Furthermore, an ink supply hole 34 is formed at the bottom of the inkreservoir 32 and communicates with an ink supply passage 43 formedthrough the glass substrate 4. Ink can be supplied from an external inksupply source to the ink reservoir 32 through the ink supply passage 43and the ink supply hole 34.

The diaphragms 33 formed at the cavity plate 3 and regulating thebottoms of the respective ink cavities 31 act as a common electrode.When a voltage is applied across the cavity plate 3 and the individualelectrodes 42 confronting the respective diaphragms 33, the diaphragms33 confronting the individual electrodes 42 on which the voltage isapplied are deflected by electrostatic force, whereby the volumes of thecavities 31 are changed and ink droplets are ejected from the nozzles21.

The nozzle 21 is a nozzle having a stepwise cross-section. That is, asmall cross-sectional circular nozzle portion 21 a (portion on a smallcross-sectional side) is formed on the front side of the nozzle 21 in anink droplet ejecting direction and a large cross-sectional circularnozzle portion 21 b (portion on a large cross-sectional side) is formedon the rear side thereof, also in that direction. Furthermore, aboundary portion therebetween is arranged as an annular stepped surface21 c. Therefore, the cross-sectional shape of the nozzle 21 is madesmaller stepwise toward the front end thereof when taken along the axialline thereof. Furthermore, the opening 21 d of the nozzle 21 at thefront end thereof is opened to the bottom of a recess 24 formed at theopposite surface of the nozzle plate 2.

Embodiment of method of manufacturing nozzle plate

FIG. 3A-FIG. 6 show an example of a process for manufacturing the nozzlelate 2. A procedure for manufacturing the nozzle plate 2 will bedescribed with reference to these figures.

(Step 1: first thermally-oxidized-film forming process)

First, as shown in FIG. 3(A), a silicon wafer 200 having a thickness of180 microns is prepared and thermally oxidized, and an SiO₂ film 210having a thickness of at least 1.2 microns is formed on a surfacethereof as a resist film.

(Step 2: first patterning process of the SiO₂ film)

Next, as shown in FIG. 3(B), the SiO₂ film 210 covering the surface 200a of the silicon wafer 200 is half-etched and a pattern 201 b and apattern 202 b are formed so as to form the large cross-sectional nozzleportion 21 b of the nozzle 21 and the shallow groove portion 22 b of theink supply port 22. Ammonium fluoride (HF : NH4F=880 ml: 5610 ml) may beused as an etchant. Furthermore, the etching depth can be set to, forexample, 0.5 micron.

(Step 3: second patterning process of the SiO₂ film)

Thereafter, as shown in FIG. 3(C), patterns 201 a and 202 a for formingthe small cross-sectional nozzle portion 21 a of the nozzle 21 and thedeep groove portion 22 a of the ink supply port 22 are formed at theportions of the patterns 201 b and 202 b as the half-etched regions ofthe SiO₂ film 210. That is, these half-etched regions are fully etchedto thereby form the patterns 201 a and 202 a where the surface of thesilicon wafer is exposed. A pattern 203 for forming the electrodethrough-hole 23 is also formed by full-etching the SiO₂ film 210together with the above patterns. Ammonium fluoride, similar to thatused above, can be also used as an etchant at this time.

A resist film of a light-sensitive resin is used as a resist film forpartially etching the SiO₂ film. The resist film is half-solidified whenit is coated and then heated, and then it is completely solidified whenit is further heated after it is exposed and developed. Thereafter, theSiO₂ film is etched as described above, whereby the resist film foretching the silicon is formed.

(Step 4: first dry-etching process)

After the patterning is applied to the SiO₂ film 210 twice,anisotropic-dry-etching is applied to the silicon wafer 200 by plasmadischarge as shown in FIG. 4(A). With this processing, the surface ofthe silicon wafer 200 is vertically etched in shapes corresponding tothe patterns 201 b, 202 b, and 203 formed at step 3, whereby grooves221, 222, and 223, having the same depth, are formed, respectively. Atthis time, a carbon fluoride (CF) gas and sulfur hexafluoride (SF₆) anbe alternately used as an etching gas. The CF gas is used to protect thesides of the grooves so that the etching does not advance thereto andthe SF₆ is used to promote the etching in the vertical direction of thesilicon wafer.

After the grooves 221, 222, and 223, each having an etching depth of,for example, 35 microns, are formed as described above, the SiO₂ film210 is removed in a thickness of 0.7 micron by etching with ahydrofluoric acid aqueous solution. As a result, the portions of thepatterns 201 b and 202 b formed at step 2 are completely removed asshown in FIG. 4(B) so that the surface of the silicon wafer 200 isexposed.

(Step 5: second dry-etching process)

Next, anisotropic-dry-etching is performed again by plasma discharge asshown in FIG. 4(C). As a result, the surface portions of the siliconwafer exposed from the patterns 201 b, 202 b, and 203 are verticallyetched in a thickness direction while maintaining the cross-sectionalshapes thereof Etching gases used at this time are the same as thoseused at step 4, and an etching depth is set to, for example, 55 microns.As a result, a nozzle groove 231 having a cross-sectional shapecorresponding to the stepwise nozzle 21 and a groove 232 having across-sectional shape corresponding to the ink supply port 22 areformed. In addition, a groove 233 having a depth half that of theelectrode disposing through-hole 23 is also formed.

Thereafter, the SiO₂ film 210 is entirely removed with a hydrofluoricacid aqueous solution (for example, HF : H₂O=1 : 5 vol, at 25° C). FIG.4(D) shows this state.

(Step 6: second thermally-oxidized-film forming process)

Subsequently, the surface of the silicon wafer 200 is again thermallyoxidized, thereby forming an SiO₂ film 240 as a resist film. It issufficient to set the thickness of the SiO₂ film 240 to 1.2 microns inthis case also.

(Step 7: third patterning process of the SiO₂ film)

Next, the portion of the SiO₂ film 240 covering the surface of thesilicon wafer 200 opposite to that processed before is etched as shownin FIG. 5(B) to thereby form a pattern 204 corresponding to the recess24 where the nozzle 21 is opened and a pattern 203A corresponding to thethrough-hole 23. The etchant used at step 2 can be also used at thistime.

(Step 8: wet-etching process)

Next, as shown in FIG. 5(C), anisotropic wet-etching is performed on theexposed portion of the silicon wafer 200 by dipping it into an etchantto form a groove 244 corresponding to the recess 24. Furthermore, agroove 233A corresponding to the through-hole 23 is formed. An etchantused at this time is a potassium hydroxide aqueous solution having aconcentration of 2 wt % and a liquid temperature of 80° C. The etchingdepth is set to, for example, 110 microns. After completion of theetching, the SiO₂ film 240 is completely removed with a hydrofluoricacid aqueous solution, as shown in FIG. 5(D), so that the grooves 231and 244, and the grooves 233 and 233A become connected respectively.

(Step 9: final thermally-oxidizing-process)

Finally, the silicon wafer is again thermally oxidized and an SiO₂ filmis formed in order to secure the ink resistant property of the siliconwafer and the intimate contact property of a nozzle surface achieved bywater repelling processing. The nozzle plate 2 can be obtained by theabove procedure.

Another Embodiment of Method of Manufacturing a Nozzle Plate

In the above embodiment, etching is conducted on one surface side of thesilicon wafer 200 for forming the nozzle plate 2 so that the fine groove231 for the nozzle 21, and the groove 223 for the electrode wiringthrough-hole 23, are formed. Furthermore, the grooves 244 and 233A,which are larger than the groove of the nozzle 21, are formed from theother surface side of the silicon wafer 200 so that the nozzle groove231 connects the groove 244 to thereby form the nozzle 21, and thegroove 233 connects the groove 233A to thereby obtain the through-hole23 at the same time.

When the etched area of the through-hole 23 is made very large in thedry-etching processes at steps 4 and 5 at the time the nozzle and thethrough-hole are formed by the above method, etching speed will bereduced and variation of etching depths will be greatly increased at thesurface of the wafer. However, these problems can be solved by themethod described below.

FIG. 7A-FIG. 10 show the manufacturing process of the nozzle plate 2 ofanother embodiment of the present invention. The manufacturing procedureof the nozzle plate 2 will be described with reference to these figures.In the following description, the description of the points overlappingwith the above embodiment will be omitted.

(Step 1-step 3)

A first thermally-oxidized-film forming process is carried out in step 1and a first patterning process for a SiO₂ film is carried out in step 2in manners similar to those in the above embodiment. A second patterningprocess for the SiO₂ film is carried out in step 3 thereafter in mannersimilar to that in the above embodiment. However, a pattern 303 forforming an electrode through-hole 23 is formed in the SiO₂ film 310 byfull-etching it into a ring groove shape so that the contour of theouter periphery of the through-hole 23 is drawn. Note that ammoniumfluoride, similar to that above, can be used as an etchant at this time.

(Step 4-step 5)

After the patterning is conducted on the SiO₂ film 310 as describedabove, anisotropic-dry-etching is applied to a silicon wafer 300 byplasma discharge, for example, by ICP discharge as shown in FIG. 8(A) inmanner similar to the above embodiment.

With this processing, in step 4, one surface side of the silicon wafer300 is vertically etched in the shapes corresponding to patterns 301 b,302 b, and 303 formed in step 3, whereby grooves 321, 322, and 323having the same depth are formed, respectively.

Thereafter, the SiO₂ film 310 is completely removed at the portions ofthe patterns 301 b, and 302 b, with a hydrofluoric acid aqueous solutionand anisotropic-dry-etching is carried out again by plasma discharge,for example, by ICP discharge as shown in FIG. 8(C). As a result, thesurface portions of the silicon wafer exposed from the patterns 301 b,302 b, and 303 are vertically etched in a thickness direction whilemaintaining the cross-sectional shapes thereof.

In each of the dry-etching processes performed twice in step 4 and step5, the groove 323 is only the outer peripheral groove for forming thethrough-hole. Thus, the etching area can be greatly reduced and etchingspeed can be increased, and the variation of the etching depths in thesurface of the wafer can be avoided.

FIG. 10 shows an example of the relationship between the etching speedand an opening ratio. The opening ratio described here is the ratio ofthe area of the etched portions of the wafer to the area of the wafer.When the opening ratio is, for example, 30%, the etching speed is 1.4μm/min, and when the opening ratio is, for example, 7%, the etchingspeed is 1.9 μm/min, as shown in FIG. 10. That is, when the openingratio is reduced from 30% to 7%, the etching speed increases about 36%.Furthermore, regarding the variation of the depths in the wafer surface,when the opening ratio is 30%, the uniformity in the wafer surface is6%, whereas when the opening ratio is 7%, the uniformity in the wafersurface is greatly improved to 4%.

Thereafter, a second thermally-oxidized-film forming process (step 6), athird patterning-process for the SiO₂ film (step 7), a wet-etchingprocess (step 8) and a final thermally-oxidizing-process (step 9) arecarried out in manners similar to those of the above embodiment, wherebythe nozzle plate is completed. Note that in step 8, a groove 333A formedby anisotropic-wet-etching penetrates to groove 333 formed in step 5,whereby the silicon of the portion surrounded by the groove 333 isremoved from the silicon wafer 300 so as to form the through-hole 23.

Other Embodiments

As other anisotropic-dry-etching methods, ECR (electron cyclotronresonance) discharge, HWP (helicon wave plasma) discharge, RIE (reactiveion etching) and the like may be used.

Furthermore, while the inkjet head used for an inkjet printer has beendescribed in the above embodiments, the present invention is not limitedthereto, and it is effective to apply the nozzle forming method of thepresent invention to the nozzle of an ejection device provided with anozzle for spraying a liquid or a gas. For example, the presentinvention may be applied to form the nozzle of a fuel injection deviceof an engine.

What is claimed is:
 1. A method of forming a nozzle for an ejectiondevice by conducting etching on a silicon monocrystalline substrate,comprising the steps of: forming a resist film on a surface of thesilicon monocrystalline substrate; forming a first opening pattern byremoving the resist film at a portion corresponding to a rear end of thenozzle; forming a second opening pattern smaller than the first patternby removing the resist film at a portion corresponding to a front end ofthe nozzle; and applying dry-etching by plasma discharge to exposedportions of the surface of the silicon monocrystalline substrate exposedby the first and second opening patterns to form the nozzle having across-section smaller stepwise from the rear end toward the front end.2. A method of forming a nozzle for an ejection device according toclaim 1, wherein said resist film comprises a silicon-oxide film.
 3. Amethod of forming a nozzle for an ejection device according to claim 1,wherein the dry-etching is carried out by alternately using a first gasand a second gas, said first gas being converted into a plasma foretching silicon by plasma discharge, and said second gas being convertedinto a plasma for suppressing the etching of silicon by plasmadischarge.
 4. A method of forming a nozzle for an ejection deviceaccording to claim 3, wherein the first gas comprises sulfur fluoride,and the second gas comprises carbon fluoride.
 5. A method of forming anozzle, which has a cross-section narrowing stepwise from a rear endtoward the front end thereof, for an ejection device by applying etchingto a silicon monocrystalline substrate, comprising the steps of: forminga resist film on a surface of the silicon monocrystalline substrate;forming a first opening pattern, which corresponds to a rear portion ofthe nozzle at a rear end thereof, in the resist film, by half-etchingthe resist film; forming a second opening pattern, which corresponds toa front portion of the nozzle at the front end thereof, by full-etchinga portion of the first opening pattern; forming a first groove having apredetermined depth by applying dry-etching to the exposed portion ofthe silicon monocrystalline substrate by plasma discharge; fully etchingthe remaining portion of said first opening so as to expose the surfaceof the silicon monocrystalline substrate; and thereafter forming asecond groove having a predetermined depth while the first grooveremains at the bottom of the second groove by applying dry-etching tothe silicon monocrystalline substrate by plasma discharge.
 6. A methodof forming a nozzle for an ejection device according to claim 5, whereinthe resist film comprises a silicon-oxide film.
 7. A method of forming anozzle for an ejection device according to claim 5, wherein thedry-etching is carried out by alternately using a first gas and a secondgas, said first gas being converted into a plasma for etching silicon byplasma discharge, and said second gas being converted into a plasma forsuppressing the etching of silicon by plasma discharge.
 8. A method offorming a nozzle for an ejection device according to claim 7, whereinthe first gas comprises sulfur fluoride, and the second gas comprisescarbon fluoride.
 9. A method of forming a nozzle for an ejection deviceaccording to claim 5, further comprising a step of: forming a thirdgroove by applying wet-anisotropic-etching to a second surface of thesilicon monocrystalline substrate opposite to the first surface to whichthe dry-etching is applied, said third groove being performed topenetrate the silicon monocrystalline substrate up to said first groove.10. A method of manufacturing an inkjet head, comprising the steps of:forming a nozzle by conducting etching on a silicon substrate,comprising the steps of: forming a resist film on a surface of thesilicon substrate, forming a first opening pattern by removing theresist film at a portion corresponding to a rear end of the nozzle,forming a second opening pattern smaller than the first pattern byremoving the resist film at a portion corresponding to a front end ofthe nozzle, and applying dry-etching by plasma discharge to exposedportions of the surface of the silicon monocrystalline substrate exposedby the first and second opening patterns to form the nozzle having across-section smaller stepwise from the rear end toward the front end;bonding a substrate on which an ink passage is formed to the lower sideof the silicon substrate provided with the nozzle so as to communicatethe nozzle with the ink passage.